Noise is part of the sea. Some of it is natural, like the sound of waves, rain, seismic activity or simply marine life. But more recently, anthropogenic noise is making itself heard. The development of industrial activities in the wake of globalization has given rise to a new form of pollution: noise pollution.
Where does noise pollution come from ?
Man-made noise comes from our ever-expanding ports. Offshore wind farms are another source of noise pollution.
When the propeller stirs up the water, the “pressure is extremely low in some places”, causing the water to boil and form “steam bubbles that grow, shrink and burst”. This phenomenon creates a deafening din at the bottom of the sea.
This noise is added to what is coming from the various submarine cables, pipe-laying and mining operations.
Not to mention the air guns used for seismic exploration.
Most anthropogenic noise comes from navigation and communication using sonars and imaging echo sounders.
Marine mammals hear sounds in the approximate range of 10 to 200 Hz. Fish hearing begins at 50 Hz and extends to 500 – 1000 Hz.
The relatively low frequencies used by humans interfere with some of the frequencies used by fish. or example, the noise produced by ships tend to be below 2 kHz. In comparison, blue whales produce vocalizations at frequencies below 100Hz. This means that their calls can be lost in the background noise produced by ships.
We can therefore deduce that the noise generated by human activity will clash with and disrupt the generation and reception of sound by marine organisms.
What are the consequences ?
The consequences of noise pollution depend on a number of factors. Each specie reacts differently to noise.
Marine animals may collaps to the bottom of the sea, becoming motionless.
Some may increase their swimming speed, or change direction or depth in the water column. It could lead to death by hemorrhage in their brain and heart. It would be a result of decompression sickness following their altered dive pattern. They act in haste, under the effect of panic, regardless of the aftermath.
Changes in school behavior also differ, ranging from closer aggregation to poorer coordination, resulting in loss of school structure or even complete dispersion.
Seismic airguns, used for seabed mapping, take their toll. The sound produced by a seismic airgun can cause permanent hearing loss, tissue damage and even death.
Powerful naval sonar could induce mass stranding. The example of more than 40 mass strandings of Cuvier’s beaked whale have been reported.
In short, a wide variety of marine animals relies on waves to find food, mate or simply navigate their way through the ocean. Noise pollution disrupts their habits, potentially endangering their health.
What could be done ?
There’s no miracle solution for avoiding noise pollution. It just has to be limited. To achieve this, a number of techniques and devices have already been put in place.
Reducing shipping traffic or, failing that, the speed of traffic, would already bring about a significant reduction in noise.
Replacing seismic air cannons would also be a step forward. Instead of using seismic air cannons, which can cause permanent hearing loss and tissue damage, we could prefer the use of “marine vibroseis”.
This device mimics the sound of waves by using vibrations rather than an explosion. This clearly limits the impact on marine life.